CMS-PAS-HIN-22-004

CMS-PAS-HIN-22-004
Dependence of two-particle azimuthal correlations on the forward rapidity gap width in pPb collisions at $ \sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}= $ 8.16 TeV
CMS Collaboration
3 June 2024

Abstract: Measurements of the Fourier coefficients ($ V_{n\Delta} $) of the azimuthal distributions of charged hadron pairs produced in pPb collisions at 8.16 TeV are presented as functions of the forward rapidity gap width ($ \Delta\eta^{\rm{F}} $) for events in which particle production is concentrated in the direction of the outgoing Pb beam. The sample includes contributions from pomeron and photon induced processes as well as nondiffractive events. The data correspond to a luminosity of 174.5 nb$^{-1}$ recorded with the CMS detector in the LHC Run 2. The mean track multiplicity decreases by 53% from the bin 0 $ \leq\Delta\eta^{\rm{F}} < $ 0.5 to that with $ \Delta\eta^{\rm{F}} > $ 2.5. The dependence of the results on the track multiplicity and the transverse momentum of the charged particles is also studied for the most forward events ($ \Delta\eta^{\rm{F}} > $ 2.5). The measured values of $ V_{1\Delta} $ are negative and decrease with $ \Delta\eta^{\rm{F}} $, while those of $ V_{2\Delta} $ are positive for the $ \Delta\eta^{\rm{F}} $ bins $ [0.5,1) $, $ [1,1.5) $, $ [2,2.5) $, and are consistent with zero elsewhere. The measured values of the elliptic flow coefficient ($ v_2 $) is provided for the $ \Delta\eta^{\rm{F}} $ bins $ [0.5,1) $, $ [1,1.5) $, $ [2,2.5) $. In the other bins, the $ v_2 $ results are consistent with zero. In these bins, upper limits at 95% C.L. are determined, ranging up to 0.13 for the most inclusive category. The values of the upper limits are similar to the values of $ v_2 $ measured in $ \gamma $p collisions with comparable multiplicity.
Links: CDS record (PDF) ; CADI line (restricted) ;

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